Tuning Twins

ENafziger said:
Not a stupid question, and you're not overthinking things. First off, you're way ahead of most people who just say "set the secondary at twice the boost of the primary". However, as you know, boost ratios and PR are NOT the same.

I went through this about a year ago as well, with my 62/476 install. It's somewhat hard to find helpful, technically accurate information on tuning twins (at least from what I could find). Nonetheless, here's what I've found out on mine.

You're going about it right, in that you want each turbo to share half of the "work"...and this means running equal PRs. However, from what I've experienced, it's not possible for this to happen in reality. You can adjust the wastegate on the secondary so that PRs on the two turbos match at one condition, but they won't match at any of the other conditions.

Since the secondary begins to spool much faster, its boost climbs quickly to about 10 psi before the primary begins to make a pound or two. The secondary continues to build boost faster, up to the point that its wastegate cracks. When the wastegate opens on the secondary, the primary begins to pick up speed much quicker. This (obviously) is because the primary is now receiving a larger percentage of the exhaust flow, and it's "higher quality" exaust due to the higher temperature of the wastegated exhaust...it is also beginning to get into the mass flow rate of air where it was designed to operate.

Thus, when you reach this point, the primary now begins building boost much quicker than the secondary. As such, neither of the turbos spool linearly with respect to each other. The small one spools quicker at first, and tapers off as the wastegate cracks. The big one is slow at first, and gets a kick in the pants as the secondary's wastegate opens. Because of this non-linearity, I've not found a way to maintain a constant shared PR across the speed/load operating range of the engine.

The best I've been able to do, is to set the wastegate on the secondary such that you are at a 1:1 PR ratio with the two turbos at about 75 - 80% of full horsepower. This allows the small secondary to spool quickly and get you going. At full 100% hp, the primary will be doing more work than it should; however, for daily driving, this has worked better for me. It does make the primary have a higher PR than the secondary at WOT, but it allows the PRs to be more closely matched in the 40 - 75% throttle range where I normally tow/drive/need boost at.

For an all-out-best dyno number, it may be better to match PRs at 100% load, but I've found for a daily driver/work horse, a little lower does better. For what it's worth, with my ~650 hp worth of fueling, the 476 primary never sees much more than 25 psi on a WOT run. Thus, unless you are too heavily fueled for the set of twins you have, I don't think there is much tuning to be done with the wastegate setting on the primary...as long as you aren't letting it crack before 25 or 30 psi and "wasting" exhaust energy.

Again, the above info may or may not be accurate, and may not be the best way of doing things. It's just what I've found to be true with my limited knowledge and my setup.

--Eric
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This really helps thank you
 
So if im seeing 60 psi overall, and 22 psi out of the primary, how does that sound to you guys? Hx35 & s475 w/1.32 housing. I was running the primary harder but have been playing with the gate a little.

This is running the truck with small injectors at about 75% throttle
 
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Well if you have the fuel, you are driving the primary too hard. What is the secondary gated at? At 22 psi, PR at sea level is 2.496....equaling the PR from the secondary equates to 77 psi of total boost
 
5.9 Cummins Fan said:
Well if you have the fuel, you are driving the primary too hard. What is the secondary gated at? At 22 psi, PR at sea level is 2.496....equaling the PR from the secondary equates to 77 psi of total boost
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Secondary is gated around 28-30 right now. I had it gated at 20 and was seeing 25 from the primary.I guess I always thought the primary should be doing the work!? And it may be making around 77 psi, im in the process of getting a 100 psi gauge in it. Just went to this setup and only have a 60.

I've never seen a s475 map, what psi is out of its range.

Also, I've got bigger sticks to swap in, will I need to completely retune the gate? Or will the settings stay the same with higher overall boost?
 
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jmd025 said:
Secondary is gated around 28-30 right now. I had it gated at 20 and was seeing 25 from the primary.I guess I always thought the primary should be doing the work!? And it may be making around 77 psi, im in the process of getting a 100 psi gauge in it. Just went to this setup and only have a 60.

I've never seen a s475 map, what psi is out of its range.

Also, I've got bigger sticks to swap in, will I need to completely retune the gate? Or will the settings stay the same with higher overall boost?
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30-32psi was the max I was told to run. Anything above is out of range.
 
The S475 will be fine longevity wise even at 40-45 psi, it just starts to add more and more waste heat to the air charge the higher you go in boost pressure.

I think the best way to tune them is to get your truck on a load cell dyno like a super flow and play around with wastegate settings till you figure out what it takes to make the most horsepower.

Then I'd tune it by driving on the street at various settings to see where it's the most responsive and drive-able.

Somewhere between those two settings is going to be a compromise of best overall useable horsepower.

For a street truck, I think I'd lean more in the direction of spool-up and response vs peak horsepower.
 
Big Blue24 said:
The S475 will be fine longevity wise even at 40-45 psi, it just starts to add more and more waste heat to the air charge the higher you go in boost pressure.

I think the best way to tune them is to get your truck on a load cell dyno like a super flow and play around with wastegate settings till you figure out what it takes to make the most horsepower.

Then I'd tune it by driving on the street at various settings to see where it's the most responsive and drive-able.

Somewhere between those two settings is going to be a compromise of best overall useable horsepower.

For a street truck, I think I'd lean more in the direction of spool-up and response vs peak horsepower.
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If you keep the charger in the high efficieny area of its map it should spool nice, yeah you can push a lot more air out of them and more air is more air. If I was building a competition setup I wouldn't give much thought to balancing them, just get as much air out of them as possible so I understand where you're coming from.
 
jmd025 said:
Secondary is gated around 28-30 right now. I had it gated at 20 and was seeing 25 from the primary.I guess I always thought the primary should be doing the work!? And it may be making around 77 psi, im in the process of getting a 100 psi gauge in it. Just went to this setup and only have a 60.

I've never seen a s475 map, what psi is out of its range.

Also, I've got bigger sticks to swap in, will I need to completely retune the gate? Or will the settings stay the same with higher overall boost?
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Thoughts on this ?

Im seeing WAY more boost than expected with these 150s! Looking at the ED wastegates..... anybody wanna chime in on them, how them mount, how they work, $$$:thankyou2:
 
this is a VERY help fulll thread!! thanks to all you guys! but i do have a few questions not a big turbo guy but a thread of mine a guy told me a stocker/s475 kit would work awesome. but i have a htb2 62/14... is there anyway this could be ran with a s475 or should i change it?? thanks!
 
c0mmins4 said:
this is a VERY help fulll thread!! thanks to all you guys! but i do have a few questions not a big turbo guy but a thread of mine a guy told me a stocker/s475 kit would work awesome. but i have a htb2 62/14... is there anyway this could be ran with a s475 or should i change it?? thanks!
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a 62 over a 475 is a very powerful combination...run it! :rockwoot:
 
people always say that the secondary is what really tells the tell on how twin setups will spool. not entirely true. on my truck, super b over a box stock S475 would not even think about lighting untill 2300rpm and was full lit at 2500 rpm. with a 1.32 ar and a turbin of 96mm, the secondary has a really tough time trying to pull air threw a charger with that large of a turbin for such little fueling that i have. just went to a S475 with a 1.1 ar and a 87 turbin. will be on the truck tomorrow. with what i noticed with the box stock 475, if i set the secondarys wastegate to start to crack at 25psi, i could only make around 34psi overall at the manifold. now if i set it to crack at 40psi, i was seeing 52psi at the manifold. just to much turbin for my setup i guess along with a big ar. even though my secondary is only 57mm, most would say that would be a fast spooling setup. not the case because you have to factor in the size of the primary as well. just my .2
 
inline6power said:
people always say that the secondary is what really tells the tell on how twin setups will spool. not entirely true. on my truck, super b over a box stock S475 would not even think about lighting untill 2300rpm and was full lit at 2500 rpm. with a 1.32 ar and a turbin of 96mm, the secondary has a really tough time trying to pull air threw a charger with that large of a turbin for such little fueling that i have. just went to a S475 with a 1.1 ar and a 87 turbin. will be on the truck tomorrow. with what i noticed with the box stock 475, if i set the secondarys wastegate to start to crack at 25psi, i could only make around 34psi overall at the manifold. now if i set it to crack at 40psi, i was seeing 52psi at the manifold. just to much turbin for my setup i guess along with a big ar. even though my secondary is only 57mm, most would say that would be a fast spooling setup. not the case because you have to factor in the size of the primary as well. just my .2
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Doesn't sound like you had the fuel for them,
 
5.9 Cummins Fan said:
Doesn't sound like you had the fuel for them,
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Mach 1, hrvp, drag comp,. Even though the sticks are on the small side, with drag comp on kill it still wouldn't even come close to spooling. That should be plenty of fuel down low to get that set rolling.

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inline6power said:
people always say that the secondary is what really tells the tell on how twin setups will spool. not entirely true. on my truck, super b over a box stock S475 would not even think about lighting untill 2300rpm and was full lit at 2500 rpm. with a 1.32 ar and a turbin of 96mm, the secondary has a really tough time trying to pull air threw a charger with that large of a turbin for such little fueling that i have. just went to a S475 with a 1.1 ar and a 87 turbin. will be on the truck tomorrow. with what i noticed with the box stock 475, if i set the secondarys wastegate to start to crack at 25psi, i could only make around 34psi overall at the manifold. now if i set it to crack at 40psi, i was seeing 52psi at the manifold. just to much turbin for my setup i guess along with a big ar. even though my secondary is only 57mm, most would say that would be a fast spooling setup. not the case because you have to factor in the size of the primary as well. just my .2
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My He351 (60mm) over HT4B (83mm) compound turbo setup spools nice and fast!
The HT4B has a huge turbine wheel, much larger than the 96x88 wheel on your S475. It does take a while to get full boost in the cold pipe between stages and there is definitely lag as far as full power/full boost, but there is almost no lag in the 0-25 psi range which is plenty for about 300 whp.



I wonder if your 57mm over 475 had a leaking wastegate or something. A large atmosphere turbo will take longer to get up to full boost, but you should have great 0-25psi boost and throttle response with a small manifold charger.

Be sure to post your results with the new tighter turbine wheel on your 475 atmosphere charger.
 
Will post results tonight. With the super b as a single item would light around 1550 in second gear. The old 475 setup wouldn't light till 2300 in third

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Signature600 said:
Something was off...that set should have been rocking on before 2000RPM

Chris
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I agree but after talking to ed, and forced they both agreed that the 1.32 housing and the 96 wheel was what my problem was so I am anxious to see if they were right. It was weird cause like I said as a single the b rocked in spool up but as soon as I put the bottom charger on it all went away. No boost leaks, so I have no clue what else would cause it to not spool. Only thing is changed was putting the bottom charger on.

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inline6power said:
Mach 1, hrvp, drag comp,. Even though the sticks are on the small side, with drag comp on kill it still wouldn't even come close to spooling. That should be plenty of fuel down low to get that set rolling.

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When I had mach 6's with my 62/71/13ss over 475/96/1.36 and ppump it still didt spool like I wanted.

Even with mach 7s and a vp I still wasn't happy.

Now with the 6x.016s its a different story. Not saying for you to go that route, just saying.
 
bsmith said:
When I had mach 6's with my 62/71/13ss over 475/96/1.36 and ppump it still didt spool like I wanted.

Even with mach 7s and a vp I still wasn't happy.

Now with the 6x.016s its a different story. Not saying for you to go that route, just saying.
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Yup really starting to feel like I don't have enough fuel

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Well think that I found the problem. Will report more tomorrow

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